
XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
PRELIMINARY
REV. P1.0.1
398
N
OTE
:
The E3_Data_Out[2:0] output pins of the Terminal
Equipment is electrically connected to the TxNib[2:0] input
pins.
The XRT74L73 will latch the data, residing on the Tx-
Nib[2:0] input pins, on the rising edge of the TxNibClk
signal.
In this case, the Terminal Equipment has the respon-
sibility of providing the framing reference signal by
pulsing the Tx_Start_of_Frame output pin (and in
turn, the TxFrameRef input pin of the XRT74L73)
"High" for one bit-period, coincident with the first bit of
a new E3 frame. Once the XRT74L73 detects the ris-
ing edge of the input at its TxFrameRef input pin, it
will begin generation of a new E3 frame.
Finally, the XRT74L73 will always internally generate
the Overhead bits, when it is operating in both the E3
and Nibble-parallel modes. The XRT74L73 will pull
the TxOHInd input pin "Low".
The behavior of the signals between the XRT74L73
and the Terminal Equipment for E3 Mode 5 Operation
is illustrated in Figure 173 .
How to configure the XRT74L73 into Mode 5
1.
Set the NibIntf input pin "High".
2.
Set the TimRefSel[1:0] bit-fields (within the
Framer Operating Mode Register) to "01" as illus-
trated below.
3.
Interface the XRT74L73, to the Terminal Equip-
ment, as illustrated in Figure 172 .
F
IGURE
173. B
EHAVIOR
OF
THE
T
ERMINAL
I
NTERFACE
SIGNALS
BETWEEN
THE
XRT74L73
AND
THE
T
ERMINAL
E
QUIPMENT
(E3 M
ODE
5 O
PERATION
)
p
Terminal Equipment Signals
RxOutClk
Tx _Start_of_Frame
E3_Nib_Clock_In
E3_Data_Out[3:0]
Payload Nibble [1059]
Overhead Nibble [0]
XRT74L73 Transmit Payload Data I/F Signals
E3 Frame Number N
E3 Frame Number N + 1
Note:
Terminal Equipment pulses
“xFrameRef
the E3 Frame Boundary.
” in order to denote
RxOutClk
TxFrameRef
TxNibClk
TxNib [3:0]
Nibble [1059]
Overhead Nibble [0]
E3_Overhead_Ind
TxOH_Ind
TxOH_Ind pulses high for 4 Nibble periods
FRAMER OPERATING MODE REGISTER (ADDRESS = 0X00)
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
Local Loopback
DS3/E3*
Internal LOS
Enable
RESET
Interrupt Enable
Reset
Frame Format
TimRefSel[1:0]
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
0
0
1
0
1
0
0
1